Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$243.89	12.279%	$273.8373	$273.84	$273.85	$273.80
Purchase #2	$79.77	12.492%	$89.7349	$89.73	$89.75	$89.70
Purchase #3	$73.69	11.801%	$82.3862	$82.39	$82.40	$82.40
Purchase #4	$72.27	4.464%	$75.4961	$75.50	$75.50	$75.50
Purchase #5	$177.43	6.763%	$189.4296	$189.43	$189.45	$189.40
Purchase #6	$246.99	4.127%	$257.1833	$257.18	$257.20	$257.20
Purchase #7	$44.91	5.614%	$47.4312	$47.43	$47.45	$47.40
7 purchase totals =	$938.95		$1,015.4986	$1,015.50	$1,015.60	$1,015.40